1. Technical Field
The present application relates to an integrated semiconductor device including a sensor or sensors for sensing and identifying analytes in a sample under investigation.
2. Description of the Related Art
The demand for microsensors of small dimensions has led to the study of integrated solutions that use techniques and knowledge acquired in the manufacture of semiconductors. In particular, detection and diagnostic devices of a disposable type, which may be connected to external apparatuses for chemical and biochemical analyses, have been studied.
Detection and diagnostic devices, utilizing microsensors, comprise a solid substrate, generally of a flat type, bearing a chip, to which particular sensors are connected. These sensors may be sensitive to various analytes, including, for example biomolecules (DNA, RNA, proteins, antigens, antibodies, hormones, etc.), micro-organisms or parts thereof (bacteria, viruses, spores, cells, etc.), and chemicals (oxygen, carbon monoxide, carbon dioxide, glucose, etc.). These microsensors are generally of a type that have limited use, either in the number of times a particular microsensor is used, or in what the microsensor is designed to detect.
For example, a common limited use microsensor is used in a handheld blood glucose meter for diabetics. Checking a person's blood glucose level usually involves a painful prick of a finger to draw out a droplet of blood. The drawn blood is placed in contact with a testing strip, which has a transducer in the form of various electrodes that are sensitive to a chemical reaction between the glucose in the blood and glucose oxidase on one of the electrodes. Signals from the electrodes are detected and processed to determine a blood glucose number that is displayed on a screen to the user.
Miniaturization of microsensors translates into smaller sample volumes and requires smaller device dimensions. With the smaller sample volumes and smaller device dimensions, the electric signal produced by an electrochemical sensor can decrease to the order of nano- or pico amperes. With such small electric signals and the need for accurate and reproducible results, controlling the conditions at which the measurements are taken becomes increasingly important.
Conditions such as temperature are known to directly affect the rate of chemical reactions. For example, there is an optimum temperature above which the reaction rate between glucose and glucose oxidase does not increase. This temperature sensitivity results in an increasing current output from the transducer as the temperature approaches the optimum reaction temperature and a decreasing current response as the temperature increases beyond the optimum reaction temperature. By controlling the temperature of the microsensor in the local region where the chemical reaction occurs, the current output from the transducer can be maximized which will result in increased sensitivity and a reduction in the effect of interfering signals.
The temperature at which a microsensor is used can affect the accuracy of the sensor in other ways. For example, if the sensor is calibrated at a specific temperature and the testing is carried out at a different temperature, the accuracy of the measurement can be adversely affected.
In addition, in some bio- or chemical microsensors, the analyte is required to diffuse through a membrane to reach the transducer. The permeability of the membrane can depend on the identity of the diffusing species and the temperature. When the permeability of the membrane is affected by temperature, the accuracy of the measurement will decrease when the measurement is carried out at a temperature different from the calibration temperature.